For practicing purposes, you could consider a VBox / OVM based setup at home. We have used those for Hands On Labs in the course of Oracle Open World more than once. I recommend you use a machine with at least 8GB memory and dual core (HT enabled) processors. Some configuration examples: Lenovo Laptop, ThinkPad, 8GB, 320GB HDD, i5 dual core, 2.5 GHz, Win 7 or a Mac Mini, latest version, i5 dual core, 2.3GHz and 8GB memory would do the trick for a two node cluster. Note that I mention the hosting OS in case you use VBox. For OVM based setups you either have to use a dual boot system or use a dedicated machine. You will be somewhat restricted with respect to the hardware failures you can impose on this system obviously (due to the VM setup), but for practicing purposes, you should find those environments sufficient, I think. Also see: RAC on OVM templates: http://www.oracle.com/technetwork/server-storage/vm/rac-template-11grel2-166623.html

You would be required atleast 4 GB RAM and 400 GB HDD with 2*dual Core processor for better installation of 11gR2 (rest 11gR1/10gR2 is not required that much hardware)
Another thing you require is VirtualBox/ Vmware, Personally I prefer to have VirutalBox as it is very ligtweight and well supported for shared disks.